The present invention relates to an apparatus for separating particulate solids from liquids in general, and more particularly to an apparatus for removing water from and for drying granules, especially granules of synthetic plastic material granulated under water.
Material granulated under water is present, after such granulation, in a large volume of water in form of a mixture therewith. The granules, prior to their further use, must be separated from water and/or dried. The separation of water from the granules and the drying of the latter have heretofore created some problems, particularly since the separating devices had to be rather huge in view of the substantial volume of water to be separated from the granules during each separating operation.
In order to improve this unsatisfactory situation, there have been already proposed, in the commonly owned U.S. Pat. No. 3,797,661, a method of separating granulates from a liquid and an apparatus capable of performing such a method, particularly for use in drying of synthetic plastic materials which have been granuled under water. There, it has been proposed to dry the granules of synthetic plastic material on a sieve by means of a gas, the amount and/or speed of which are the same over the major portion of the sieve and the advancement energy is resolved in a flow-through component which forces the water through the sieve and a propagating component which propels the granulate over the sieve.
The arrangement for performing the above method includes two parallel lateral walls of which one is formed with a gas-inlet opening, and a blower mounted between the parallel lateral walls for rotation. The arrangement further includes a curved sieve wall surrounding the blower and having interruptions for the entrance of the granulate-water mixture and the discharge of the dry granulate, such interruptions communicating with inlet and outlet conduits, respectively. The inlets and outlets and the associated interruptions ae spatially separated from one another, and a gas-guiding sheet extends from the inlet interruption toward the outlet interruption and so partially surrounds the blower that the distance thereof from the blower increases in the direction of rotation of the blower.
When the granulate-water mixture enters into the region of the sieve, it is first separated from the excessive water which is not tied, in one way or another, to the granules. After that, the granulate which has been rid of the excessive water is pressed against the sieve by the pressurized gas issuing from the blower which advances at a much higher speed than the granulate. As a result of this, the water present in the interstices between the granules is continuously detached from the granulate, despite the low mechanical engagement, and is conducted, together with a part of the pressurized gas, through the sieve. Inasmuch as the advancing pressurized gas imparts a movement component to the granulate on the sieve, the adhesive water film is continuously detached from the individual granules and also expelled through the sieve. Finally, the remaining water vaporizes.
The above-mentioned method achieves, in a relatively small arrangement, a quick separation of water from granulate, as a result of a stronge aeration of the predried granulate. As a result of this, the granulate is very quickly and by resorting to simple means, brought into a condition suitable for the storage and further use of the granulate.
The two lateral walls may be part of a casing from which the expelled or separated water is withdrawn by means of a water conduit, and a source of vacuum may communicate with such water conduit in order to accelerate the penetration of the water through the sieve, so that, at any time, a sufficiently large amount of the pressurized gas flows through the sieve and, consequently, entrains the desired amount of water.
In order to improve the economies of the method, it has also been proposed to separately intercept or collect the pressurized gas penetrating through the sieve and the water expelled through the sieve, and to separately prepare such media after the discharge thereof from the casing for reintroduction thereof into the process as separately circulating media.
The advantage of this method is to be seen in the fact that the amount of the drying or separating pressurized gas is constant over the major part of the sieve. However, experience with this type of arrangement has shown that the performance of this arrangement still leaves much to be desired, particularly in terms of efficiency and throughput for given dimensions of the arrangement.